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Re: [Cfrg] Discuss/standardize Preview extension to AEAD abstraction?

Peter Gutmann <pgut001@cs.auckland.ac.nz> Fri, 04 December 2015 03:15 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: Damien Miller <djm@mindrot.org>, Bryan Ford <brynosaurus@gmail.com>
Thread-Topic: [Cfrg] Discuss/standardize Preview extension to AEAD abstraction?
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Date: Fri, 04 Dec 2015 03:15:09 +0000
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Subject: Re: [Cfrg] Discuss/standardize Preview extension to AEAD abstraction?
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Damien Miller <djm@mindrot.org> writes:

>At the other end, I want to, given enough of the header of that blob, be able
>to determine a) how many bytes I need to read to get the whole thing, b) how
>much space I'll need to extract the plaintext (if any) and c) how much space
>I'll need to extract the AAD (if any).

+1.  This is my big gripe with SSH, it doesn't allow you to do this.

(An elegant trick, mentioned to me by someone else off-list, is to
speculatively read ahead, or at least non-blocking over-read each block, by 5
bytes so you optionally get the info on the next TLS data block before you
need it.  Then you can read and decrypt in-place, for an overhead of close to
1 network I/O/kernel transition/whatever your TCP stack does per block).

Peter.

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